2004-2007 Cadillac CTS-V General Discussion Discussion, noise still coming from the back...need help. in Cadillac CTS-V Series Forum - 2004 - 2007; The first problem is still there. I took it to jiffy lube and asked specifically for the GM oil and ...

The first problem is still there. I took it to jiffy lube and asked specifically for the GM oil and additive. They ended up putting Pennzoil and I'm not even sure if they put additive. Does the Pennzoil work because the noise never went away.

Re: noise still coming from the back...need help.

Originally Posted by 4DoorZ06

The first problem is still there. I took it to jiffy lube and asked specifically for the GM oil and additive. They ended up putting Pennzoil and I'm not even sure if they put additive. Does the Pennzoil work because the noise never went away.

Pennzoil lists synthetic and non-synthetic GL-5 specification gears oils. All of those I found indicate that they are suitable for limited-slip differentials which means they come with some additive in them. However, there is no way to know that the friction coefficient is correct for any particular differential. Since yours may still be making noise, I would add more additive. Most autoparts stores carry one brand or another of gear oil friction modifier. Just drain out some the existing fluid and add the additive. (or ask Jiffy to do so.)

(The original Techinical Service Bulletin on this issue (2004) actually suggested removing the limited-slip clutch packs from the differential and soaking them in the additive to cure the condition. While that is no longer recommended, it does suggest that some extra additive may required to cure the issue once it developements.)

Re: noise still coming from the back...need help.

I had a terrible rubbing noise coming from the rear diff. It was when the car was in gear and turning at slow speed, like when parking. It was like a grinding/rubbing noise that sounded like bad bushings or bearings. It was driving me nuts since I had recently had the diff serviced and used Royal Purple. Another mechanic I know, who has a GTO recommended Amsoil with the slip lock additive. He also told me it would take like 2 days for the noise to abate after changing the fluid. I told him straight that his suggestion sounded like so much bullshit...I mean no "fluid" could possibly make a noise like THAT go away...and whats with the 2 days??? 2 days for "oil" to make a HUGE rubbing noise go away?

Well, wouldn't ya know it. The guy was like a fortune teller. We put the Amsoil in and right away I noticed the sound started changing...it wasn't so...hair raising. Sure enough, 2 days later, the sound was completely gone. Unreal.... From oil.

Re: noise still coming from the back...need help.

To answer your question, I actually called the mechanic who cured mine, and this is what he said: "You really need the AC Delco 35/90 full synthetic with their "friction modifier". About 2 qts. of the 35/90 and 2 ounces of the friction modifier. Because the the AC Delco is hard to find or available only through the dealer, we used Amsoil 35/90 synthetic on yours with 2 ounces of the "slip lock additive."

I can tell you that it cured mine, and it was was making so much noise it was setting my teeth on edge. Again, it was so hard to believe that mere oil could have such a profound effect, but it did....I'm certainly not claiming this is your issue. I'm just relating my story, and a fluid change is a lot cheaper than wrenching on a rear end!